Embodiments of the present disclosure relate generally to wireless power transfer devices. Specifically, embodiments of the present disclosure relate to methods and systems for detecting foreign objects that may interfere with a wireless charging device.
Wireless power is now widely used for charging mobile devices, charging electric vehicles, powering biomedical devices, and other applications. Wireless power transfer is implemented using a power transmitter that transfers power to a power receiver. The power receiver is often integrated with or attached to the end device being charged by the wireless power transfer system, although the power transmitter device typically is not physically attached to the end device. Electronics connected to the transmitter transform power from a power source (whether alternating current or direct current) to a suitable form to drive a power transmitter coil in the transmitter. The power is then transferred from the power transmitter coil to a power receiver coil using inductive coupling. Electronics in the receiver then condition the power from the receiver coil, generating suitable output to power the device or charge a battery connected to the device.
In an ideal wireless power transfer system, the transmitted power and received power are equal, meaning that no power is lost during transmission. However, because power is transmitted using an electromagnetic field, energy can be lost in the system when the field interacts with metal or electrically conductive parts not configured to power or charge the device. Not only does the resulting power loss lead to a reduction in efficiency of the wireless charging system, but it can also cause heating of the metal parts. This heating can, in turn, damage the device or pose a threat to the safety of the user.